The present invention relates to a lubricant used for lubrication between solid frictional surfaces.
Petroleum liquid lubricants are generally used for lubrication of, for example, bearings, gears, pistons, and cylinders in various machines such as engines, electric motors and generators. However, if these petroleum lubricants are imprudently leaked or abandoned, they sometimes cause pollution of natural environment. On the other hand, as liquid lubricants which do not Cause pollution of natural environment and are substitutable for the conventional petroleum lubricants, there are proposed lubricants comprising an aqueous solution containing not less than 0.1% by mass of a saccharide such as purified sugar, crude sugar, molasses-containing sugar or the like (e.g., JP-A-2001-172664).
However, in the case of the above so-called aqueous lubricants containing saccharides, all of the saccharides not necessarily provide good lubrication characteristics (low frictional characteristics, high wear resistance, anti-seizure characteristics), and some of the saccharides are inferior particularly in anti-seizure characteristics. As a result of the subsequent research conducted by the inventors, it has been found that sucrose is a saccharide to be used for non-pollution lubricants and can give excellent lubrication characteristics, particularly, anti-seizure characteristics, and the inventors developed aqueous lubricants using sucrose as the saccharide and filed a patent application (Japanese Patent Application No. 2002-86260).
Thus, the invention of aqueous lubricants which use sucrose as a saccharide could produce excellent results in improvement of lubrication characteristics of aqueous lubricants. However, the inventors have conducted further research in an attempt to attain further improvement of lubrication characteristics, particularly, further reduction of friction coefficient.
Therefore, the object of the present invention is to provide lubricants which cause no environmental pollution and are substitutable for conventional lubricants and which are excellent in lubrication characteristics, particularly, low frictional characteristics.